The present invention relates to a process for selectively compressing granular material in a molding box and, more particularly, a process wherein the granular material is compressed by a series of pressure surges applied over the granular material.
The packing of granular molding materials for the purposes of producing factory molds is old and well known in the prior art. It is customary when packing the granular molding materials to provide a predetermined amount of a compressed medium over the molding box which acts upon the granular material in the molding box to compress same. A typical arrangement is disclosed in German Patent Specification No. 19 61 234 which discloses a typical process for packing granular molding material wherein the packing of the molding material is effected by the expansion of a high pressure gas within the molding apparatus. During the packing process the gas, which is stored under pressure in a reservoir, is transferred within a very short time interval to the surface of the granular material so as to impact on the surface of the material being compressed. The pressure is maintained on the surface of the granular material for a predetermined time interval and thereafter the pressure is reduced by means of venting.
Processes of the foregoing type result in a casting mold hardness profile which decreases from the pattern to the back of the mold as a consequence of the compression characteristics. While this hardness profile provides ideal conditions for degasification of the casting molds, there are a number of disadvantages which result from such a process. These disadvantages include (a) irregularity of the hardness of the mold; (b) noise resulting from the one time, sudden compression surge; and (c) compression defects due to the high sand flow velocity.
Naturally, it would be highly desirable to provide a process which allows for the selective compression of the granular material in a casting mold which would eliminate the disadvantages noted above with regard to processes heretofore known.
Accordingly, it is a principal object of the present invention to provide a process for compressing granular materials in a molding box.
It is a particular object of the present invention to provide a process for compressing granular material wherein the material is compressed by sequential pressure surges.
It is a further object of the present invention to provide a process as set forth above wherein the mold hardness profile of the compressed mold decreases from the pattern to the back of the mold.
Further objects and advantages of the present invention will appear hereinbelow.